Hebeloma arcticum Beker & U. Eberh. sp. nov.

Eberhardt, Ursula, Beker, Henry J., Borgen, Torbjorn, Knudsen, Henning, Schuetz, Nicole & Elborne, Steen A., 2021, A survey of Hebeloma (Hymenogastraceae) in Greenland, MycoKeys 79, pp. 17-118 : 17

Hebeloma arcticum Beker & U. Eberh. sp. nov. Figs 22 , 23

Type.

Greenland. Sisimiut : at the bridge on the road to the airport (approx. 66.944317N, 53.670444W, alt. approx. 0 m a.s.l.), 14 Aug. 2016, H. Knudsen (HK16.119) (Holotype: C-F-104149; Database Record: HJB17673 ; Genbank: ITS = MW445587 , Tef1 a = MW452584 and RPB2 = MW452593 ) .

Diagnosis.

Favoring arctic type habitats with many cheilocystidia clavate-stipitate and rather strongly dextrinoid but indistinctly ornamented spores.

Etymology.

arcticus (adj. Latin), meaning the arctic, to emphasize the habitat within which this mushroom has been discovered.

Macroscopic description.

Cap (1.7-) 2.4-2.9 (-3.8) cm, plano-convex, with or without suggestion of obtuse umbo, with decurved margin then applanate, only weakly viscid even after heavy rainfall, dull, almost glabrous, marginal zone whitish pale due to a fine adpressed tomentum, often eroded, usually bicolored, center ochre, paler towards the margin becoming very pale brownish, hardly hygrophanous but a few hygrophanous dots. Lamellae emarginate with tooth, ventricose, number of lamellae {L} 36-44, up to 4 mm wide, initially pale, darker (clay buff) at maturity with whitish fimbriate edge and usually some watery droplets or droplets visible with a x10 lens. Stem (2.8-) 4.1-4.4 (-6.0) × 0.5-0.7 (-0.9) cm, to 0.6-0.9 cm at base, whitish fibrillose to pruinose, cylindrical, narrowly fistulose, downwards pale yellowish to pale brownish when rubbed. Context firm, thick particularly in center, whitish pale, watery when moist, in age slightly brownish downwards in stipe. Smell weakly herbaceous-raphanoid. Taste mild. Spore print at most clay buff (Munsell 10YR6/4; in TB 90.071).

Microscopic description.

Spores amygdaloid, ellipsoid or ovoid, on ave. (across eight collections) 10.8-12.0 × 6.4-6.9 µm, ave. Q = 1.65-1.83, (for the holotype, measuring 102 spores, 5% to 95% percentile range 10.4-13.2 × 5.9-7.2 µm with median 11.9 × 6.5 µm and ave. 11.9 × 6.5 µm and S.D. for length 0.84 µm and for width 0.39 µm, and Q value 5% to 95% percentile range 1.57-2.04, with median 1.83 and ave. 1.83 with S. D. 0.14), yellow brown, guttulate, not papillate, almost smooth (O1), perispore not loosening (P0), distinctly to strongly dextrinoid (D2D3). Basidia (20) 22-37 × 6-10 μm; ave. Q 3.0-3.7, (for the holotype 25-37 × 7-9, ave. Q 3.6), mostly four-spored. Cheilocystidia mainly clavate-stipitate, sometimes clavate-ventricose, more rarely capitate-stipitate, occasional apical or median wall thickening, sometimes septate (occasionally clamped), on ave. 36-57 × 6-9 (apex) × 4-5 (middle) × 4-6.5 (base) µm, ratios A/M = 1.5-2.3, A/B = 1.2-2.0, B/M = 1.0-1.4, (for the holotype, width near apex, 5% to 95% percentile range 6.5-8.3 µm, with median 7.4 µm and ave. 7.4 µm with S.D. 0.63 µm and over all 45 × 7.4 (apex) × 5 (middle) × 6.5 (base) µm). Pileipellis an ixocutis, up to 90 µm thick (measured from exsiccata), hyphae up to 6 µm broad, none encrusted; trama elements beneath subcutis isodiametric to ellipsoid or thick sausage-shaped, up to 17.5 µm wide. Caulocystidia similar to cheilocystidia, up to 90 µm long.

Other collections examined.

S-Greenland: Paamiut, 62.01°N, 49.4°W, 31 Aug 1986, T. Borgen (TB86.277A, C-F-103571), 10 m, with S. arctophila , 62.01°N, 49.4°W, 4 Sep 1990, T. Borgen (TB90.083, C-F-103555), 10 m, with Salix glauca and Bistorta vivipara in fenland. Paamiut, 62.01°N, 49.4°W, 1 Sep 1990, T. Borgen (TB90.071, C-F-103483), 10 m, with Salix glauca and Bistorta vivipara . Paamiut, near cemetery, 61.9941°N, 49.6666°W, 21 Aug 2008, T. Borgen (TB08.153, C-F-106751), 15 m, with Salix glauca . W-Greenland: Kangerlussuaq, Ringsødalen, Ringsøen, 66.9853°N, 50.9464°W, 9 Aug 2016, T. Borgen (TB16.095, C-F-103584), 180 m, with Salix glauca . Kangerlussuaq, Ringsødalen, Ringsøen, 66.9853°N, 50.9464°W, 9 Aug 2016, H. Knudsen (HK16.044, C-F-104080), 180 m, with Salix glauca . Kangerlussuaq, Russels Glacier, 67.0977°N, 50.2318°W, 12 Aug 2000, S.A. Elborne (SAE-2000.021-GR, C-F-108472), 220 m, with Salix glauca .

Distribution.

This is a new species known from a number of records in the Low Arctic zone in southern and western Greenland. The fact that it was collected several times independently may indicate that it is quite common in these areas.

Habitat and ecology.

Eight collections, seven with Salix glauca one with S. arctophila . Most collections are from mineral-poor ground.

Notes.

The mainly clavate-stipitate cheilocystidia indicate that this species belongs in H. sect. Denudata and there in H. subsect. Crustuliniformia .Few species of the subsection have almost smooth spores or spores that are rather strongly dextrinoid. The combination of almost smooth and rather strongly dextrinoid spores is unique in this subsection. Molecular results support its placement within this subsection. Within H. sect. Denudata , based on the spore characters, H. arcticum is readily identifiable. To be noted is also the unusual shape of the spores; while many spores are amygdaloid, many others appear more ellipsoid or cylindrical, again uncommon for this section of Hebeloma . As Figs 5A-B show, H. arcticum is well distinct from related taxa and is in a supported clade (Fig. 5B ) with other members of H. subsect. Crustuliniformia , but is not a member of the H. alpinum -complex. The clade of the species is supported by 100% bootstrap in the analysis of three loci (Fig. 5B ), but based on current knowledge, ITS alone is sufficient to recognize the taxon; in the ITS tree (not shown) calculated prior to concatenation of the data, H. arcticum received 84% bootstrap support.

Figures

Figure 5. A Pruned quasi-median network of the Hebeloma alpinum complex, H. arcticum and H. louiseae. Circles shared by two or more taxa or collections from two regions, from Greenland (G) or collected elsewhere, are divided according to the number of representatives for each class B ML result for Hebeloma subsect. Crustuliniforme, based on concatenated ITS, RPB 2 and Tef 1 a data, rooted with H. louiseae. Thick branches indicate bootstrap support of at least 80 % (450 bootstrap replicates). Species are represented by three collections (if available); Hebeloma arcticum by four collections including the holotype.

Figure 22. Hebeloma arcticum A HK 16.119 (holotype), photograph H. Knudsen B distribution of cited collections.

Figure 23. Hebeloma arcticum HK 16.119 (holotype) A spores x 1600 and B spore ornamentation x 1600 in Melzer's reagent C spores and D spore ornamentation x 1600 in KOH E basidia cheilocystidia and F cheilocystidia x 1000 in Melzer's reagent G caulocystidia x 500 in KOH H cutis x 125 in KOH. Scale bars: 5 µm (A-F); 10 µm (G); 50 µm (H); microphotographs H. K. J. Beker.